The cheapest option would be to sell you car and buy a Ninja 250 with cash. You could see 80mpg if you change to a smaller rear sprocket and hypermile. Those motorcycles are cheap to purchase, maintain, insure, and they hold their value.
The best sound system you are likely ever to buy is a high quality set of headphones. If you can fit them under your helmet, the audiophile problem should be taken care of...
Assuming gas @ $3.75 and your 500 mile a week commute, a Ninja 250 could save you ~$42 a week in gas alone. Your operating cost would plummet even more after registration, insurance, and maintenance are factored in. You would need protective gear and a license, but otherwise it would be cheap. Just a thought...
- LostCause